Multi-layer circuit board and method of manufacturing the same

ABSTRACT

A multilayer wiring board comprising a mother wiring board and a carrier wiring board, in which all of the composing layers have IVH structure. The mother wiring board ( 11 ) is formed in the manner that a plurality of resin-impregnated-fiber-sheets having mother wiring layers ( 13 ) and first inner-via-hole conductors ( 14 ) for connecting the wiring layers ( 13 ) each other are laminated. The mother wiring board ( 11 ) comprises a base board ( 11   a ) and container board ( 11   b ) having an opening for forming a cavity ( 15 ). The carrier wiring board ( 16 ) has lands ( 17 ) for mounting LSI bare chips, wirings ( 18 ), a plurality of carrier-board-wiring-layers ( 19 ) and second inner-via-hole conductors ( 20 ) for connecting the wiring layers. ( 19 ) each other. The carrier wiring board ( 16 ) is set in the cavity ( 15 ) for electrically connecting the carrier wiring board ( 16 ) to the mother wiring board ( 11 ) by connecting carrier board electrodes ( 21 ) to mother board electrodes ( 22 ) through connectors ( 23 ) of solder balls, gold bumps or electrically conductive paste. The carrier wiring board ( 16 ) has higher wiring density at the portion where LSI bare chips are mounted, than the mother wiring board.

FIELD OF THE INVENTION

[0001] The present invention relates to a multilayer wiring board having a plurality of wiring layers and high density wirings for directly mounting high-density large-scale-integrated-circuit (hereinafter referred to as LSI) chips and the method of manufacturing the same.

BACKGROUND OF THE INVENTION

[0002] In recent years, the printed wiring boards for the high density mounting of miniaturized electronic components is actively developed under the trend of reducing size and weight of electronic equipment having high performance.

[0003] Especially the economical supply of multilayer wiring boards for high density mounting of semiconductor such as LSI chips and for high speed data processing circuit is strongly desired. In such multilayer wiring board, it is important to have high reliability on electrically connecting a plurality of layers of fine pitch wiring patterns each other and to have superior high frequency characteristics. Therefore, wiring boards having new structure and new manufacturing methods are being developed because the old ones can hardly meet such request. In the old multilayer wiring boards, wiring layers are electrically connected each other by conductors of through-hole structure formed by drilling, and etching on copper coated boards or metal plating.

[0004] A method proposed by the Japanese Patent Application Laid Open No. H06-268345 is a resinous multilayer wiring board in which all composing layers have inner-via-hole (hereinafter referred to as IVH) structure for connecting wiring layers each other. The electrical conductors of the IVH structure is formed in the manner that electrically conductive material is filled into the IVHs. In this method, the reliability of electrical connection is improved, also the IVHs can be formed just under the lands for mounting electronic components, and can be formed at any portion between the wiring layers, accordingly the size reduction of the wiring board and high density mounting can be realized.

[0005] In general, the substrate for the above wiring board is formed in the manner that aramid non-woven fabric or the like is impregnated with epoxy resin that works as insulation material. The resinous multilayer wiring board using the above substrate has the advantages of low expansion, low permittivity and light, therefore the substrate is widely used for electronic equipment for reducing the size and weight.

[0006] However, in general, in the above resinous multilayer wiring board having IVH structure on all of the composing layers, the wiring density such as wiring pitch and wiring width are determined to have similar wiring patterns on all of the wiring boards, also the wiring patterns is formed by conventional photolithography on a resinous substrate whose top side and bottom side are plated with metal such as copper or the like.

[0007] Therefore, in the above conventional method shown in FIG. 14, the wiring density of the area for mounting resin-packaged LSI chips 3 is determined by the shape or size of discrete components such as a chip resister, a chip capacitor and the like.

[0008] For reducing further the size of a wiring board 4, it is advisable to mount the LSI chips 3 in the form of bare, for which the wiring density of the mounting area have to be high enough. However, if the high density area for the LSI bare chips and the relatively low density area for the discrete components are formed on one wiring board, the production yield of the wiring board becomes extremely low, which causes high cost of the wiring board.

[0009] For addressing this problem, several method are proposed. Hereinafter the proposed methods and still existing problems are described.

[0010] The method of the Japanese Patent Application Laid Open No. H05-48231 is that high density wiring board is set in a cavity formed on a wiring board having low wiring density. In this method, the two wiring board are electrically connected each other by aligning electrical conductors of respective wiring boards, which are formed in through-holes of respective wiring boards. However, since all of the composing layers have not IVH structure, the wiring boards are electrically connected each other through the electrical conductors exposed at the ends of the respective wiring boards. Accordingly the obtainable wiring density is not high enough in this method.

[0011] The method of the Japanese Patent Application Laid Open No. H09-46015 is that two wiring boards having respectively different wiring density are laminated. In this method, there are problems of the decrease of the speed of signal flow due to the increase of the length of the wiring lines, the increase of total thickness of the wiring boards, and that the flatness is insufficient or the height is not low enough.

[0012] The method of the Japanese Patent Application Laid Open No. H09-199824 is that an opening or a cavity is formed on a multilayer wiring board in which all of the composing layers have IVH structure. This method intended to realize high density mounting of electronic components and to decrease the height by mounting the components in the opening or in the cavity. However, in this method, the mounted components are resistors, capacitors and the like, and, it is not intended to set a wiring board having IVH structure in the opening or in the cavity. Therefore, this method can not realize the improvement of wiring density and the production efficiency.

[0013] The method of the Japanese Patent Application Laid Open No. H010-4153 is that a staircase-shape cavity is formed on a wiring board, and LSI chips are set in the cavity, and, the LSI chips are connected to wiring layers of the wiring board by a wire-bonding method. In this method, there are problems of decrease of speed of signal flow due to the increase of the length of the wiring lines, the increase of size due to unused space of the cavity, and the problems of no improvement on mounting density and production efficiency as in the above method of No. H09-199824.

SUMMARY OF THE INVENTION

[0014] The present invention aims to provide an economical and miniaturized multilayer wiring board by further utilizing the advantages of resinous multilayer wiring board in which all of the composing layers have IVH structure, and to provide the method of manufacturing the multilayer wiring boards having the above features. For that, a mother wiring board and a carrier wiring board having respectively different wiring density for fitting to respective mounted components are manufactured separately in former manufacturing processes and are integrated in a latter manufacturing processes, which suppresses the manufacturing cost of the wiring board, also further miniaturizes the wiring board by enabling high density direct mounting of LSI bare chips.

[0015] In more detail, the mother wiring board has relatively low wiring density for mounting discrete components such as resistors, capacitors and the like, accordingly the cost for manufacturing the mother wiring board is relatively low. On the other hand, the carrier wiring board has high wiring density for mounting LSI bare chips. The mother wiring board is electrically connected to the carrier wiring board by setting the carrier wiring board in a cavity formed on the mother wiring board. The above structure and the manufacturing method of the multilayer wiring board enable to obtain an economical multilayer wiring board having high performances such as high speed data processing and highly reliable electrical connection.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 shows the cross section of a portion of a multilayer wiring board in a first exemplary embodiment of the present invention,

[0017] FIGS. 2(a) and (b) show the cross sections of a portion of a multilayer wiring board in a second exemplary embodiment of the present invention,

[0018] FIGS. 3(a) and (b) are cross sectional views showing the assembling process of a base board in the method of manufacturing a multilayer wiring board in a third exemplary embodiment of the present invention,

[0019] FIGS. 4(a) and (b) are cross sectional views showing the assembling process of a container board in the method of manufacturing the same,

[0020] FIGS. 5(a) and (b) are cross sectional views showing the assembling process of a mother wiring board in the method of manufacturing the same,

[0021] FIGS. 6(a) and (b) are cross sectional views showing the assembling process of a carrier wiring board in the method of manufacturing the same,

[0022] FIGS. 7(a) and (b) are cross sectional views showing the assembling process of a multilayer wiring board in the method of manufacturing the same,

[0023] FIGS. 8(a) and (b) are cross sectional views showing the assembling process of a base board of a multilayer wiring board in a fourth exemplary embodiment in the method of manufacturing the same,

[0024] FIGS. 9(a) and (b) are cross sectional views showing the assembling process of a container board in the method of manufacturing the same,

[0025] FIGS. 10(a) and (b) are cross sectional views showing an other structure of a container board of the forth exemplary embodiment in the method of manufacturing the same,

[0026] FIGS. 11(a) and (b) are cross sectional views showing the assembling process of a mother wiring board in the fourth exemplary embodiment in the method of manufacturing the same,

[0027] FIGS. 12(a) and (b) are cross sectional views showing the assembling process of a carrier wiring board in the method of manufacturing the same,

[0028] FIGS. 13(a) and (b) are cross sectional views showing the assembling process of a multilayer wiring board in the method of manufacturing the same, and

[0029]FIG. 14 is a cross sectional view showing an example that electronic components are mounted on a conventional multilayer wiring board in which all of the composing layers have IVH structure.

DESCRIPTION OF PREFERRED EMBODIMENTS First Exemplary Embodiment

[0030]FIG. 1 shows the structure of a multilayer wiring board in a first exemplary embodiment of the present invention. In FIG. 1, a mother wiring board 11 in which all of the composing layers have IVH structure is formed by laminating a plurality of substrates 12 produced in the manner that aramid fiber or the like is impregnated with heat-curing-type-resin such as epoxy resin or the like, and the resin is cured. Mother-board-wiring-layers are electrically connected each other by first via-hole conductors (hereinafter referred to as first IVH conductor) 14 formed in the through-holes of the substrates 12. The mother wiring board 11 comprises a base board 11 a and a container board 11 b. As shown in FIG. 1, the container board 11 b has at least one opening for forming a cavity 15 in which a carrier wiring board 16 is set. In this case, it is advisable to fill up the remaining space of the cavity 15 with sealing resin for obtaining a long life characteristic by protecting, from the air, the portions where the mother wiring board 11 is electrically connected to the carrier wiring board 16.

[0031] The carrier wiring board 16 has lands 17 for mounting electronic components such as LSI bare chips and wirings 18 on the top side, a plurality of carrier-board-wiring-layers 19 therein, and second inner-via-hole conductors (hereinafter referred to as second IVH conductor) 20 for electrically connecting the wiring layers each other. All layers of the carrier wiring board 16 have IVH structure as in the case of the mother wiring board 11.

[0032] The circuit of the mother wiring board 11 are electrically connected to that of the carrier wiring board 16 in the manner that carrier board electrodes 21 formed on the bottom side of the carrier wiring board 16 are connected to mother board electrodes 22 formed on the top side of the base board 11 a that composes the bottom of the cavity 15 of the mother wiring board 11, through connectors 23 of solder balls, gold bumps or electrically conductive paste.

[0033] At least the uppermost wiring board on which LSI bare chips are mounted out of a plurality of wiring boards of the carrier wiring board 16 has higher wiring density than any wiring board of the mother wiring board 11.

[0034] The features and the effects of the multilayer wiring board of this exemplary embodiment is described hereinafter.

[0035] A first feature is that the above multilayer wiring board comprises two types of wiring boards, i.e., the mother wiring board 11 on which discrete components such as resistors, capacitors, coils and connectors are mainly mounted for forming a main circuit, and the carrier wiring board 16 on which LSI bare chips are mainly mounted. The number of the carrier wiring boards 16 and the corresponding number of the containing cavities 15 formed on one mother wiring board 11 are determined according to the required functions in the application to electronic equipment, or, a plurality of LSI chips can be mounted on one carrier wiring board, also an electronic circuit module can be formed on one carrier wiring board.

[0036] A next feature is that the wiring density is different between the mother wiring board 11 and the carrier wiring board 16. The wiring density of the mother wiring board 11 is relatively low, i.e., the wiring pitches of the mother wiring board 11 are determined according to the shape or the terminal pitches of mounted discrete electronic components. While the wiring density of the carrier wiring board 16 is higher than that of the mother wiring board 11, i.e., the pitches of the wiring of the top side and the IVH conductors of the carrier wiring board 16 is determined according to the extremely fine electrode pitches of LSI bare chips for the flip-chip-bonding, of the LSI bare chips on the carrier wiring board 16, accordingly, the manufacturing cost of the carrier wiring board 16 becomes high because high technology on designing and manufacturing are required.

[0037] As described above, by manufacturing the low cost portion, viz., the mother wiring board 11 separately, and by limiting the high cost portion to the carrier wiring board 16 as in this exemplary embodiment, the total cost of the multilayer wiring board can be suppressed, furthermore, since the LSI bare chips can be mounted directly on the carrier wiring board 16, the size including the thickness of the whole wiring board can be reduced and the cost can also be reduced.

[0038] In other words, in the present invention, by the direct mounting of the LSI bare chips in stead of mounting resin or ceramic packaged LSI chips, the size including the thickness can be further reduced, also, by manufacturing separately the extremely fine pitch portion for directly mounting LSI bare chips, the production yield of the multilayer wiring board can be improved, accordingly the production cost is reduced, comparing the method of forming a high wiring density portion and a low wiring density portion on one wiring board.

Second Exemplary Embodiment

[0039] Hereinafter a second exemplary embodiment of the present invention is described referring to FIGS. 2(a) and (b), in which the same reference numerals are applied as in the first exemplary embodiment for the same composing portions. The difference of this exemplary embodiment from the first exemplary embodiment is on the shape of the cavity 32 formed on the mother wiring board 31, and on the shape of the carrier wiring board 33 set in the cavity 32 for electrically connecting to the mother wiring board 31.

[0040] In more detail, as shown in FIG. 2(a), the portion of the cavity 32 of a container board 31 b has a staircase-shape though a base board 31 a composing the mother wiring board 31 is almost same as the base board 11 a of the first exemplary embodiment. On the respective exposed flat portions of the staircase, container board electrodes 34 are formed. The carrier wiring board 33 has a reversed staircase-shape for fitting to the staircase-shape of the container board 31 b, and has carrier board electrodes 35 formed on the exposed flat portions of the reversed staircase, the carrier electrodes 35 are for connecting to the container board electrodes 34. In this exemplary embodiment, fewer base board electrodes 22 are formed on the exposed portion of the top side of a base board 31 a than those in the first exemplary embodiment because the container board electrodes 34 are formed on the container board 31 b.

[0041] The cavity 32 of the multilayer wiring board of the present invention has four sides though only right and left sides of a staircase-shape are shown in FIG. 2(a) because the illustration shows the cross section of the multilayer wiring board. Therefore the staircase structure can be formed on one, two, three or four sides of the cavity 32.

[0042] The features and the effects of the multilayer wiring board having the above structure are described hereinafter. As shown in FIG. 2(a), stairs of the mother wiring board 31 and those of the carrier wiring board 33 fit each other in the manner that the mother board electrodes 22 and 34 on the flat portions of the mother wiring board 31 are directly connected to the carrier board electrodes 35 on the flat portions of the carrier wiring board 33. Accordingly the wiring structure inside the carrier wiring board 33 can be simplified and the total length of the wiring lines can be reduced. Therefore, the size of the multilayer wiring board can be reduced and the data processing speed can be increased by the decrease of wiring resistance.

[0043] Hereinafter an example of the above feature is described referring to FIG. 2(b). As shown in FIG. 2(b), when a power source wiring layer 13 e and a grounding wiring layer 13 f are formed on respectively different layers of a plurality of mother-board-wiring-layers, these can be electrically connected respectively, with short distance, to a power source terminal 34 e and a grounding terminal 34 f formed on the corresponding stairs of the staircase structure of the carrier wiring board 33. Accordingly, the power source impedance and the grounding impedance can be reduced.

[0044] In the same manner as above example, since the terminals of the carrier wiring board can be connected to the corresponding wiring layers on the corresponding stairs of the mother wiring board, larger tolerance on the alignment of electrical connection can be obtained. Accordingly, the production yield in respect to the above electrical connection can be improved.

Third Exemplary Embodiment

[0045] A method of manufacturing multilayer wiring board in a third exemplary embodiment of the present invention is described hereinafter referring to FIG. 3 through FIG. 7, which show the method of manufacturing a multilayer wiring board described in the first exemplary embodiment. FIGS. 3(a) and (b) show an assembling process of a base board composing a mother wiring board, FIGS. 4(a) and (b) show an assembling process of a container board composing the mother wiring board, FIGS. 5 (a) and (b) show an assembling process of the mother wiring board, FIGS. 6(a) and (b) show an assembling process of a carrier wiring board, and FIGS. 7(a) and (b) show an assembling process of the multilayer wiring board of the first exemplary embodiment.

[0046] First, the assembling process of the base board 11 b is described hereinafter referring to FIGS. 3(a) and (b). As shown in FIG. 3(a), dual-side wiring boards 36 and 37 have wiring layers 13 a and 13 b, and, 13 c and 13 d on the top side and the bottom side of each of the substrates that compose the wiring boards, also have first conductors 14 that electrically connect the wiring layers each other.

[0047] The substrates on which the wiring layers are formed are generally produced in the manner that non-woven sheet made of glass, aramid, aromatic polyester and the like is impregnated with heat-curing-type-resin of epoxy resin, BT resin (trade name of Mitsubishi Chemical), polyimide resin, modified PPE resin and the like (hereinafter the substrate is referred to as resin-impregnated-fiber-sheet).

[0048] On the top side of the dual-side-wiring-board 36, mother board electrodes 22 are formed, which are connected to carrier board electrodes (ref. 21 of FIG. 6) when the carrier wiring board is set in the mother wiring board. An intermediate connector 38 has a plurality of necessary number of through-holes formed on the resin-impregnated-fiber-sheet of prepreg state that composes the connector 38, and has first IVH conductors formed by filling electrically conductive paste or the like into the through-holes.

[0049] The base board 11 a of FIG. 3(b) having four wiring layers 13 a, 13 b, 13 c and 13 d connected each other by the first IVH conductors 14 is formed in the manner that the intermediate connector 38 is sandwiched by the dual-side-wiring-boards 36 and 37, and these are precisely aligned, and heated and pressed together in up-and-down directions.

[0050] In FIG. 3, the diameter of the first IVH conductor of the dual-side-wiring-board 36 is different from that of the dual-side-wiring-board 37. However, the dimension of the diameters can be the same between the two, or can be various dimensions according to requirement.

[0051] Second, the assembling process of the container board 11 b is described hereinafter referring to FIGS. 4(a) and (b). In FIG. 4(a), dual-side-wiring-boards 39 and 40 have wiring layers 13 a and 13 b, and, 13 c and 13 d respectively on the top side and the bottom side of each of the resin-impregnated-fiber-sheets that compose the wiring boards, and have first IVH conductors 14 that electrically connect the wiring layers each other, also have at least one opening 15 a respectively. When a plurality of openings 15 a are formed on the respective dual-side-wiring-boards 39 and 40, the sizes of the respective openings are determined to correspond to the sizes of the carrier boards (ref. 16 of FIG. 6).

[0052] An intermediate connector 41 has a plurality of necessary number of through-holes formed on the resin-impregnated-fiber-sheet of prepreg state that composes the connector 41, and has first IVH conductors 14 formed by filling electrically conductive paste or the like into the through-holes, also has an opening 15 a corresponding to the openings of the dual-side-wiring-boards 39 and 40.

[0053] The container board 11 b of FIG. 4(b) having four wiring layers 13 a, 13 b, 13 c and 13 d connected each other by the first IVH conductors 14 is formed in the manner that the intermediate connector 41 is sandwiched by the dual-side-wiring-boards 36 and 37, and, these are precisely aligned, and heated and pressed together in up-and-down directions.

[0054] Third, the assembling process of the mother wiring board 11 is described hereinafter referring to FIGS. 5(a) and (b). In FIG. 5(a), an intermediate connector 42 has an opening 16 a formed through the resin-impregnated-fiber-sheet that composes the connector 42, in which the size of the opening corresponds to that of the container board 11 b, also has first IVH conductors 14. The mother wiring board 11 of FIG. 5(b) in which all of the composing layers have IVH structure, and, the base board 11 a and the container board 11 b are electrically connected each other by the first IVH conductors 14 of the intermediate connector 42 is formed in the manner that the intermediate connector 42 is sandwiched by the base board 11 a and the container board 11 b, and these are precisely aligned, heated and pressed together in up-an down directions, in this process the intermediate connector 42 cures.

[0055] Fourth, the assembling process of the carrier wiring board 16 is described hereinafter referring to FIGS. 6(a) and (b). In FIG. 6(a), an uppermost dual-side-wiring-board 43 has lands 17 and wirings 18 on the top side, a carrier-board-wiring-layer 19 a on the bottom side, and second IHV conductors 20 that electrically connect the wirings 18 and the lands 17 to the carrier-board-wiring-layers 19. The lands 17 are formed to be high density wiring pattern for mounting LSI bare chips having fine pitches.

[0056] A dual-side-wiring-board 44 has carrier-board-wiring-layers 19 a and 19 c respectively on the top side and the bottom side of the resin-impregnated-fiber-sheet that composes the wiring board 44, also has second IVH conductors 20. A dual-side-wiring-board 45 has carrier-board-wiring-layers 19 d on the top side, carrier board electrodes 21 on the bottom side, and second IVH conductors 20. Intermediate connectors 46 and 47 respectively have second IVH conductors 20 for electrically connecting the dual-side-wiring-boards 43, 44 and 45 each other.

[0057] A carrier wiring board 16 of FIG. 6(b) in which all of the composing layers have IVH structure is formed in the manner that the above wiring boards and connectors are placed in the turn of FIG. 6, and are precisely aligned, heated and pressed together in up-and-down directions, in this process the intermediate connectors 46 and 47 cure.

[0058] Finally, as shown in FIG. 7, the multilayer wiring board of the present invention comprising different types of wiring boards can be obtained by setting the carrier wiring board 16 in the cavity 15 of the mother wiring board 11, in which carrier board electrodes 21 formed on the bottom side of the carrier wiring board 16 are electrically connected to mother board electrodes 22 formed on the bottom of the cavity 15, through connectors 23 of solder balls, gold bumps or electrically conductive paste.

[0059] In this case, the carrier wiring board 16 can be set in the cavity 15 of the mother wiring board 11 after LSI chips are mounted on the lands 17 of the carrier wiring board 16. Also, FIG. 1 and FIG. 7(b) show the examples that the top of the mother wiring board and the top of carrier wiring board are on a same level. However, the top of carrier wiring board 16 can be formed to be at lower level than the top of the mother wiring board 11 so that the thickness of the multilayer wiring board can be suppressed by reducing the increase of thickness caused by the protection resin layer for covering the LSI bare chips mounted on the lands 17.

Fourth Exemplary Embodiment

[0060] A method of manufacturing multilayer wiring board having staircase structure in a fourth exemplary embodiment of the present invention is described hereinafter referring to FIG. 8 through FIG. 13, in which the same reference numerals are applied as in FIG. 1 and FIG. 2 for the same composing portions.

[0061] FIGS. 8(a) and (b) show an assembling process of a base board composing a mother wiring board, FIGS. 9(a) and (b) show a assembling process of a container board composing the mother wiring board, FIGS. 10(a) and (b) show an assembling process of a container board having an other structure for composing a mother wiring board, FIGS. 11(a) and (b) show an assembling process of a mother wiring board by connecting the base board of FIG. 8 to the container board of FIG. 9. FIGS. 12(a) and (b) show an assembling process of a carrier wiring board, and, FIGS. 13(a) and (b) show an assembling process of a multilayer wiring board of the fourth exemplary embodiment having a staircase structure by assembling the mother wiring board and the carrier wiring board.

[0062] First, the assembling process of the base board 31 a is described referring to FIGS. 8(a) and (b). In FIG. 8(a), dual-side-wiring-boards 48 and 49 respectively have wiring layers 13 a and 13 b, and, 13 c and 13 d on the top side and the bottom side of the respective resin-impregnated-fiber-sheets that compose the wiring boards, also have first IVH conductors that connect the wiring layers each other. On the top side of the dual-side-wiring-board 48, mother board electrodes 22 for connecting to the carrier electrodes (described later) of the carrier wiring board are formed. Intermediate connector 50 has first IVH conductors formed in the manner that electrically conductive paste or the like is filled into a plurality of necessary number of through-holes formed on the resin-impregnated-fiber-sheet of prepreg state.

[0063] The base board 31 a of FIG. 8(b) having the four wiring layers 13 a, 13 b, 13 c and 13 d electrically connected each other by the first IVH conductors is formed in the manner that the intermediate connector 50 is sandwiched by the dual-side-wiring-boards 48 and 49, and these are precisely aligned, heated and pressed together in up-and-down directions.

[0064]FIG. 8 shows an example that the dual-side-wiring-boards 48 and 49 have the IVH conductors of respectively different diameters. However the dimension of the diameters can be the same, or can be various dimensions according to requirement. The base board 31 a of FIG. 8(b) of this exemplary embodiment has fewer number of electrodes 22 than in the base board 11 a of FIG. 3(b) of the first exemplary embodiment.

[0065] Second, the assembling method of container board 31 b of this exemplary embodiment having a cavity of a staircase-shape is described hereinafter referring to FIGS. 9(a) and (b). In FIG. 9, single-side-wiring-boards 51, 52 and 53 respectively have wiring layers 13 a, 13 b and 13 c on one side of each of the resin-impregnated-fiber-sheets that compose the wiring boards, first IVH conductors 14, and at least one respective openings 15 a, 15 b and 15 c that are different each other in size. A dual-side-wiring-board 54 composing a lowermost wiring board of the container board 31 b has wiring layers 13 d and 13 e, and, IVH conductors 14.

[0066] Intermediate connectors 55, 56 and 57 respectively sandwiched by the wiring boards 51, 52, 53 and 54 as shown in FIG. 9 respectively have first IVH conductors formed in a plurality of necessary number of through-holes formed on the respective resin-impregnated-fiber-sheets of prepreg state that compose the intermediate connectors, also, respectively have openings 55 a, 56 a and 57 a whose sizes correspond to those of wiring boards locating at respective upper sides.

[0067] The staircase-shape container board 31 b of FIG. 9(b) having five wiring layers, three contact stairs and first IVH conductors connecting wiring layers 13 a, 13 b, 13 c, 13 d and 13 e each other is formed in the manner that above wiring boards and the intermediate connectors are placed in the turn as shown in FIG. 9, and these are precisely aligned and heated and pressed together in up-and-down directions.

[0068] Third, the assembling process of an other example of a staircase-shape container board is described hereinafter referring to FIGS. 10(a) and (b). A staircase-shape container board 108 of FIG. 10(b) having six wiring layers and two contact stairs is formed in the manner that dual-side-wiring-boards 101, 102 and 103 respectively having wiring layers 104 a and 104 b, 104 c and 104 d, and, 104 e and 104 f, and different size openings 105 a, 105 b, and 105 c are laminated, in which intermediate connectors 106 and 107 having openings 106 a and 107 b whose sizes correspond to those of the wiring layer of respective upper sides are sandwiched by the wiring boards 101, 102 and 103 as shown in FIG. 10.

[0069] In the container wiring board of this exemplary embodiment, as described above, the number of contact stairs and the number of wiring layers are determined according to the circuit structure of applied electronic equipment or the type of mounted LSI bare chips by forming the container board with the combination of the single-side-wiring-boards and the dual-side-wiring-boards.

[0070] Fourth, an assembling method of the mother wiring board 31 of this exemplary embodiment is described hereinafter referring to FIGS. 11(a) and (b). The mother wiring board 31 of FIG. 11(b) in which all of the composing layers have IVH structure is formed in the manner that an intermediate connector 58 is sandwiched by the above base board 31 a and container board 31 b, and these are precisely aligned, and heated and pressed together in up-and-down directions, in this process the intermediate connector 58 cures. In this case, the intermediate connector 58 has an opening whose size is substantially same as the opening 15 d of the bottom of the container board 31 b, also has first IVH conductors 14.

[0071] Fifth, an assembling method of a carrier wiring board 33 of FIG. 2 is described referring to FIGS. 12(a) and (b). In FIG. 12(a), a first dual-side-wiring-board 60 has the structure that lands 17 and wirings 18 are formed on the top side, a carrier wiring layer 19 a and carrier board electrodes 35 a are formed on the bottom side, and second IVH conductors 20 are formed in through-holes of the resin-impregnated-fiber-sheet that composes the wiring board 60. The lands 17 are formed to be a high density pattern for corresponding to the terminal pitches of mounted LSI chips.

[0072] A second wiring boards 61 and a third wiring board 62 are respectively formed in the manner that carrier-board-wiring-layers 19 b and 19 c, and, carrier electrodes 35 b and 35 c are respectively formed on one side of the resin-impregnated-fiber-sheets that compose the wiring boards, and, second IVH conductors 20 are respectively formed in the through-holes of the respective resin-impregnated-fiber-sheets. A fourth wiring board 63 is formed in the manner that carrier electrodes 35 d are formed on the bottom side of the resin-impregnated-fiber-sheet that compose the wiring board 63, and second IVH conductors 20 are formed in the through-holes of the resin-impregnate-fiber-sheets.

[0073] Intermediate connectors 64, 65 and 66 respectively have second IVH conductors 20 formed by filling electrically conductive paste or the like into through-holes formed on the respective resin-impregnated-fiber-sheets of prepreg state. The sizes of the respective intermediate connectors are determined to be smaller than the wiring boards located at the upper side of the respective intermediate connectors so that the electrodes formed on the respective wiring boards are exposed as shown in FIG. 12(b).

[0074] The reversed-staircase-shape carrier wiring board 33 having four contact stairs, five wiring layers and exposed electrodes 35 a, 35 b, 35 c and 35 d formed on the flat portions of the four contact stairs is formed in the manner that the above boards and the conductors are placed in the turn of FIG. 12, and these are precisely aligned, heated and pressed together in up-and-down directions.

[0075] The reversed-staircase-shape carrier wiring board of this exemplary embodiment can be formed with the other combination of single-side-wiring-boards and dual-side-wiring-boards than that of the above description, as in the case of the staircase-shape container wiring board 31 b.

[0076] Finally, as shown in FIG. 13, the multilayer wiring board of the present invention comprising different types of wiring boards can be obtained by setting the carrier wiring board 33 in the staircase-shape cavity 32 of the mother wiring board 31, in which the carrier board electrodes 35 formed on the exposed flat portions of the carrier wiring board 33 are connected to the mother board electrodes 22 and 34 formed on the flat portions of the cavity 32, through connectors 23 of solder balls, gold bumps or electrically conductive paste.

[0077] As described above, in the present invention, a low cost mother wiring board having relatively low wiring density is manufactured separately from a high cost carrier wiring board having high wiring density for directly mounting LSI bare chips at the former manufacturing processes, and these are integrated and electrically connected each other in the latter manufacturing processes for completing a multilayer wiring board. Accordingly the cost for the designing and the manufacturing of the multilayer wiring board can be reduced, also the structure can be modified for fitting to respective requirements, also, superior electrical characteristics and high reliability of electrical connection can be obtained. 

What is claimed is:
 1. A multilayer wiring board comprising: (a) a mother wiring board having: (a-1) a wiring formed on the surface thereof; (a-2) a plurality of wiring layers formed therein; (a-3) inner-via-hole conductors for electrically connecting said wiring layers each other; (a-4) at least one cavity on the surface thereof; and (b) a carrier wiring board; wherein said carrier wiring board is set in said cavity of said mother wiring board, and electrically connected to said mother wiring board.
 2. A multilayer wiring board comprising: (a) a mother wiring board having: (a-1) a wiring formed on the surface thereof; (a-2) a plurality of wiring layers formed therein; (a-3) inner-via-hole conductors for connecting said wiring layers each other; (a-4) at least one staircase-shape cavity, wherein at least one side thereof has a staircase-shape formed in the manner that the stairs are continuously formed by every layer of said wiring layers, or discontinuously formed in the manner that some layers of said wiring layers form no stair; and (b) a staircase-shape carrier wiring board fitting to said staircase-shape cavity of said mother wiring board; wherein said staircase-shape carrier wiring board is set to said staircase-shape cavity of said mother wiring board, and electrically connected to said mother wiring board.
 3. A multilayer wiring board comprising: (a) a mother wiring board having: (a-1) a wiring formed on the surface thereof; (a-2) a plurality of wiring layers formed therein; (a-3) inner-via-hole conductors for connecting said wiring layers each other; (a-4) at least one staircase-shape cavity, wherein at least one side thereof has a staircase-shape formed in the manner that the stairs are continuously formed by every layer of said wiring layers, or discontinuously formed in the manner that some wiring layers form no stair, wherein said wiring layers include at least one electric power source layer and at least one grounding layer; and (b) a carrier wiring board having a staircase-shape; wherein said carrier wiring board is set in said staircase-shape cavity of said mother wiring board, and the connection terminals of said carrier wiring board are electrically connected to the corresponding connection terminals of said mother wiring board, wherein the electrical power source terminal and the grounding terminal of said carrier wiring board are electrically connected to said electric power source layer and said grounding layer of said mother wiring board respectively.
 4. A multilayer wiring board according to claim 1, 2 or 3, wherein said carrier wiring board has wirings on the top side and the bottom side thereof, or a plurality of wiring layers therein in addition to said wirings of the top side and the bottom side thereof, and inner-via-hole conductors for electrically connecting said wiring layers each other.
 5. A multilayer wiring board according to claim 1, 2 or 3, wherein said carrier wiring board has at least one land on the surface thereof, for mounting an electronic component.
 6. A multilayer wiring board according to claim 1, 2 or 3, wherein the wiring density formed on said mother wiring board is different from the wiring density formed on said carrier wiring board.
 7. A multilayer wiring board according to claim 1, 2 or 3, wherein said mother wiring board or said carrier wiring board has at least one wiring board having wiring density differing from the wiring density of the other wiring layers of said respective wiring boards, wherein said mother wiring board and said carrier wiring board respectively have a plurality of wiring layers.
 8. A multilayer wiring board according to claim 1, 2 or 3, wherein the top of said carrier wiring board set in said cavity of said mother wiring board locates at lower level than the top of said mother wiring board.
 9. A multilayer wiring board according to claim 1, 2 or 3, wherein said mother board electrodes formed in said cavity of said mother wiring board are electrically connected to said carrier board electrodes formed on the bottom side or on the lateral sides of said carrier wiring board through solder balls when said carrier wiring board is set in said mother wiring board.
 10. A multilayer wiring board according to claim 1, 2 or 3, wherein said mother board electrodes formed in said cavity of said mother wiring board are electrically connected to said carrier board electrodes formed on the bottom side or on the lateral sides of said carrier wiring board through gold bumps when said carrier wiring board is set in said mother wiring board.
 11. A multilayer wiring board according to claim 1, 2 or 3, wherein said mother board electrodes formed in said cavity of said mother wiring board are electrically connected to said carrier board electrodes formed on the bottom side or on the lateral sides of said carrier wiring board through electrically conductive paste when said carrier wiring board is set in said mother wiring board.
 12. A multilayer wiring board according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, wherein the material composing said mother wiring board and said carrier wiring board is same or respectively different.
 13. A multilayer wiring board according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, wherein the material composing said mother wiring board or said carrier wiring board is a resin-impregnated-fiber-sheet made of the composite of glass-fiber-nonwoven-fabric and heat-curing-type-resin, or organic-fiber-nonwoven-fabric and heat-curing-type-resin.
 14. A method of manufacturing a multilayer wiring board, which comprises the steps of: (a) forming a base board by laminating a plurality of resin-impregnated-fiber-sheets respectively having wiring layers on the surfaces thereof and inner-via-hole conductors therein; (b) forming a container board by laminating a plurality of resin-impregnated-fiber-sheets respectively having wiring layers on the surfaces thereof, inner-via-hole conductors therein, and at least one opening therethrough; (c) forming a mother wiring board having at least one cavity by laminating said base board and said container board; (d) forming a carrier wiring board by laminating a resin-impregnated-fiber-sheet having at least one land and at least one wiring on the surface thereof, and a plurality of resin-impregnated-fiber-sheets respectively having inner-via-hole conductors therein; and (e) electrically connecting said carrier wiring board to said mother wiring board by setting said carrier wiring board in said cavity of said mother wiring board. 